Blown Film Extrusion Introduction

Blown Film Extrusion Introduction
Blown film extrusion is a technology that is the most common method to make plastic films, especially for the packaging industry. The process involves extruding a tube of molten polymer through a die and inflating to several times its initial diameter to form a thin film bubble. This bubble is then collapsed and used as a lay-flat film or can be made into bags. Usually polyethylene is used with this process, and other materials can be used as blends with these polymers. A diagram of a polyethylene chain is shown in Figure 1 to the right.
Background Theory on Polymers

In the cooling step of blown film extrusion, the amorphous, transparent melt crystallizes to form a translucent, hazy, or opaque film. The point where opacity begins in the bubble is known as the frost line. 
Fig 1: Model of polytheylene chain frompolyethylene Wikipedia article.The frost line height is controlled by several parameters: the air flow, film speed, and temperature difference between the film and the surroundings. Properties of the film, such as tensile strength, flexural strength, toughness, and optical properties, drastically change depending on the orientation of the molecules. As the transverse or hoop direction properties increase, the machine or longitudinal direction properties decrease. For instance, if all the molecules were aligned in the machine direction, it would be easy to tear the film in that direction, and very difficult in the transverse direction.

The Film Blowing machine Process

Fig 2: Schematic of set-up from User:J.Chiang.

Typically, blown film extrusion is carried out vertically upwards, however horizontal and downward extrusion processes are now becoming more common. Figure 2 shows a schematic of the set-up for blown film extrusion. This procedure consists of four main steps: The polymer material starts in a pellet form, which are successively compacted and melted to form a continuous, viscous liquid. This molten plastic is then forced, or extruded, through an annular die. Air is injected through a hole in the center of the die, and the pressure causes the extruded melt to expand into a bubble. The air entering the bubble replaces air leaving it, so that even and constant pressure is maintained to ensure uniform thickness of the film. The bubble is pulled continually upwards from the die and a cooling ring blows air onto the film. The film can also be cooled from the inside using internal bubble cooling. This reduces the temperature inside the bubble, while maintaining the bubble diameter. After solidification at the frost line, the film moves into a set of nip rollers which collapse the bubble and flatten it into two flat film layers. The puller rolls pull the film onto windup rollers. The film passes through idler rolls during this process to ensure that there is uniform tension in the film. Between the nip rollers and the windup rollers, the film may pass through a treatment centre, depending on the application. During this stage, the film may be slit to form one or two films, or surface treated. Advantages Blown film generally has a better balance of mechanical properties than cast or extruded films because it is drawn in both the transverse and machine directions. Mechanical properties of the thin film include tensile and flexural strength, and toughness. The nearly uniform properties in both directions allow for maximum toughness in the film.
Blown film extrusion can be used to make one large film, two smaller ones, or tubes that can be made into bags. Also, one die can make many different widths and sizes without significant trimming. This high level of flexibility in the process leads to less scrap material and higher productivity. Blown films also require lower melting temperatures than cast extrusion. Measured at the die opening, the temperature of cast film is about 220 C, where as the temperature of blown film is about 135 C. Furthermore, the cost of the equipment is approximately 50% of a cast line.

Blown Film Extrusion Disadvantages Blown film has a less effective cooling process than flat film. Flat film cooling is done by means of chill rolls or water, which have significantly higher specific heat capacities than the air that is used in the blown film cooling process. The higher specific heat capacity allows the substance to absorb more heat with less change in the substance temperature. Compared to cast film, blown film has a more complicated and less accurate method to control film thickness; cast film has a thickness variation of 1 to 2% versus the 3 to 4% for blown film. The resins used for casting typically have a lower melt flow index, which is the amount of polymer that can be forced through a standard die in 10 minutes according to a standard procedure. The melt flow index for cast film is about 5.0 g/10 min where as for blown film it is about 1.0 g/10 min. Consequently, the production rates for cast film are higher: cast film lines can reach production rates of up to 300m/min where as blown film lines are usually less than half this value. And finally, cast film has better optical properties, including transparency, haze, and gloss.

Common Problems Air entrapment between film layers and rollers – this may cause film scratching or wrinkling, or processing problems when winding up the film due to reduced friction. Possible solutions to this is using a vacuum to remove entrapped air or by using winding rolls with a diamond shaped groove in the rubber cover to increase surface area and decrease amount of entrapped air in the film. Large output fluctuations from the die – this causes thickness variations, and can be prevented by keeping the extruder clean and by using more consistently shaped pellets in the extruder. Melt fractures – these appear as roughness or wavy lines on the film surface, and can be eliminated by lowering the viscosity of the polymer melt. This can be done by increasing the melting temperature or by adding an internal lubricant to the material composition. Thickness variations in the film – this can be avoided by centering the die in the extrusion line before every run, adjusting the air speed of the cooling system, or by using heated die lips. Die lines on the surface of the film – this defect reduces the aesthetic appeal of the film, reduces optical properties, and weakens mechanical properties such as tear strength. This can usually be avoided by routinely cleaning the inner surfaces of the die and by refinishing scratched or roughened flow surfaces. Gels – these defects are small, hard globules encapsulated in the film or stuck on the film surface and reduce the aesthetic appeal of the film and cause stress concentration points which may result in premature failure. These are caused by overheating to the point of polymer degradation in the die, and can therefore be avoided by cleaning the inner surfaces of the die on a regular basis. Optimization of the Process Coextrusion One way to improve the line efficiency of blown film extrusion is to implement coextrusion. This is the process of extruding two or more materials simultaneously through a single die. The orifices in the die are arranged such that the layers merge together before cooling. This process saves time because it extrudes two or more layers at the same time, and it provides a method with fewer steps to produce multilayer films. The production rate for a coextruded multilayer film of three layers is about 65m/min, and the production rate for a single layer of blown film is about 130m/min. Thus, in order to produce 10 000m of a three layer multilayer film, it would take almost 4 hours using a single layer blown film process, and only 2 and a half hours using the coextrusion process. Furthermore, the film produced from the single layer process would require an extra step to glue the layers together using some sort of adhesive. Coextrusion is the least expensive means of producing layered films and the coextrusion system is capable of quick changeovers to minimize production line down time.

Minimizing the Melt Temperature
The efficiency of blown film extrusion can be improved by minimizing the temperature of the polymer melt. Reduction of the melt temperature causes the melt to require less heating in the extruder. Normal extrusion conditions have a melting temperature at about 190 C despite the fact that the temperature of the melt only needs to be about 135 C. However, it is not always practical to decrease the melting temperature by that much. By decreasing the melt temperature 2 to 20 C, the motor load can be decreased by about 1 to 10%. Furthermore, reduction of the melt temperature causes less need for cooling, so there is a reduced use of the cooling system. Moreover, removing heat from the bubble is usually the rate-limiting factor in this extrusion process, so by having less heat in the polymer to remove, the rate of the process can be increased, thus yielding higher productivity. A way to maintain the melt temperature at a minimum is to choose an extruder that is matched to the specific processing conditions, such as the material of the melt, pressure, and throughput.

Heated Extrusion Die Lips
Typically, solutions to melt fractures involve decreasing the output or increasing the melt temperature to decrease the shear stress in the extruder. Both of these methods are not ideal because they both reduce the efficiency of the blown film line. Heated extrusion die lips can solve this problem. This targeted heating method allows for film extruders to be run at higher production rates with narrower die gaps while eliminating melt fractures. Direct heat is applied to the surface of the polymer melt as it exits the die so that viscosity is reduced. Therefore, melt fractures, which are caused when trying to extrude too much of the polymer at one time, will no longer act as a limiting factor to increasing the production rate. Furthermore, heated die lips use less energy than increasing the melting temperature because only the surface of the melt is heated and not the bulk of the liquid. Another benefit of using heated die lips is that thickness variations can be controlled by adding heat to certain areas along the die circumference to make the film at that position thinner. This would ensure that no excess material is used.
Determine how much energy each of these processes can save per given volume of material. 

Above article from www.appropedia.org

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Make Certain You’re Going To Know Exactly What People Are Stating About Your Company

A company’s standing has always been extremely crucial. In the past, a company’s track record was normally found out about through testimonials. Whenever a person desired to find out a lot more about a business, they would ask close friends and family. Now, however, it’s easier still for them to find this information, and that may not be good for the business in the event the details are not positive. It really is crucial for an organization to actually watch their internet based track record in order to make sure prospective consumers are looking at favorable accounts about the company.

Folks today utilize the web whenever they’ll need far more information about an organization. A basic search on the web is going to offer them multiple pages together with lots of reviews with regards to even newer companies. If perhaps this information is positive, they are going to likely become a customer. Nevertheless, if perhaps the information is largely bad, it’s probable they’ll opt to go with a competitor instead. This is the reason it really is so essential for a company owner to be able to ensure the info submitted about their organization will be positive. Doing this, nevertheless, may take a considerable amount of time if they will just check out each and every review web site routinely.

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Athens – What To See And How To See It

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There are so many aspects of current civilization that were birthed in ancient Athens. Among these are theatre, philosophy, democracy, classical art and even the Olympic games. Athens is located on the southern coast of Greece and has existed for over 7,000 years providing a rich culture expressed in a diverse setting. The term diverse fits as you will find ancient relics and sites in some of the same areas where there are trendy boutiques and sidewalk cafes all mixed in together. This mixture of the very old and the new create a very unique experience provided nowhere in the world like it is provided in the ancient city of Athens. You will need to be sure your passport is up to day so if you need to add passport pages, be sure to go online and access a passport site to help you with this so you can be on you way.

World travel requires a passport but computers have simplified all passport needs. Even if you have to get an emergency passport, an online passport is available to help you. No one plans to have their travel documents lost or stolen but if this happens, help is as close as the nearest computer.

Athens is a city that contains many sites that make history come alive so this is certainly the ideal place for lovers of history to visit. High on top of the Acropolis you will find the Parthenon. This famous sight has earned the honor of being named as a World Heritage Site by UNESCO. Investigating these ruins takes you back to sights names in Greek Mythology related to gods and goddesses, the titans and many other mythological characters. Admission to this site also opens the Theatre of Dionysus, the Roman Agora and the Temple of Olympian Zeus to the traveler.

Being the birthplace of the performing arts, it is no wonder that the arts and culture are very important to the Athenians. While the National Gallery is certainly large and well known, many smaller art galleries populate the city. Athens is also host to approximately 148 theatres so if you are in the mood for a show, the difficult part will be which performance to see. Among the theatres is the famous Herodes Atticus Theatre.

Using a bike or even walking around this city is a wonderful way to see the sights. Green space is always welcome when you travel to big cities and the National Garden of Athens provides an exceptional treat. Within it can be found a small zoo, ponds with ducks, colorful flowers and beautiful landscape with no shortage of a shady tree to relax under and consider the sights of the day.

For those who would like to shop till your drop, your experience will be a little different in Athens. Rather than large malls and strip centers, you will find street vendors selling custom crafts rather than name brand items. Some of the most visited markets are found on Plaka, Kolonaki and Ermou Street. You will find endless selections of shoes, purses and jewelry if you visit here and the quality will certainly not disappoint you.

Authentic cuisine is always interesting in a foreign city and Athens is no exception to this rule. Known for their souvlaki, which is comprised of grilled meat, veggies and a special yogurt sauce, this Athenian staple is considered a treat by all who try it.

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Steer Clear of Trouble and Do Not Take Pointless Chances

At times, on some days, it appears as if the USA is almost bordering on being a police state. You will find tales regarding older men who ended up imprisoned for selling orchids plus booked with federal criminal accusations, plus testimonies about youngsters whose homemade lemonade stands were knocked over by the law enforcement. It often appears just as if sound judgment flew away and bullying and of course frustration took their very own position. Needless to say, having an open perimeter as well as what are nearly undoubtedly countless crooks racing in the country, it is easy to realize why many law enforcement officials may well be about edge and really feel they need to end up taking intense actions, only to protect their own personal wellbeing.

Meaning the average woman and man now ought to proceed out into the streets as well as byways of the nation plus run by themselves using extreme caution until finally things with any luck , wind down. Display esteem to the peace officer you encounter and don’t do anything whatsoever in order to upset these people. Even when you have made an error in judgment, simply go along utilizing the actual authority on hand. It’s possible to acquire a criminal defense lawyer in the future to help you to sort things out in the court, and that is much smarter than seeking to make your own personal type of justice in the public. People that adopt that tactic will likely end up in jail. If you were arrested for some sort of crime, ask around and learn who the great lawyers tend to be and hire one that’s experienced in that particular area related to your own challenge. If you are presented a ticket with regard to careless/reckless driving, receive a traffic ticket attorney. Did you rob a store? Some sort of criminal lawyer. Driving while impaired? Some sort of dwi lawyer.

Conduct your behavior in a law-abiding plus respectful method, and then the probability is excellent you will be in the position to “actually come in beneath the radar” and not get embroiled in any issues. Show your immaturity, though, by simply speeding or possibly peeling rubber or running red lights you may have a respected blue light circling in your rear view reflection quickly. Our country’s incarceration rate is the earth’s highest. That figure isn’t one you should especially choose to enhance. For that reason, end up being smart in how you behave your behavior, remain cautious, and do not end up in compromising scenarios.

Generate A Little Bit More Money Working From Home

An individual who stays at home with the youngsters may well not desire to entirely give up making money in order to accomplish that. Despite the fact that they will mainly be caring for the kids, there are instances when they’re able to sit down at the computer and accomplish a small amount of work to be able to make the funds they will require. A parent or gaurdian who really wants to do that will certainly need to investigate a handful of the ways they’re able to help to make cash from home.

Composing a weblog or perhaps producing posts for other’s blogs may be a wonderful income source. Cash back web pages can easily supply them with some money also. They may additionally desire to think about investing some money. Whenever they will have extra time in the house, they’re able to look at sites to learn far more regarding how to invest their own money. The correct investments could help their particular money grow considerably as well as can make it simpler for them to actually bring in a little extra cash. All these methods, and much more may be mixed as well so they can earn nearly as much cash as is possible while working from home.

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Perform A Little Research In Order To Check Out Investment Possibilities

Someone who really wants to get started investing might learn about plenty of different companies they are going to wish to invest in. However, they will need to be very careful with just how they’ll really invest their funds as they are going to need to ensure they’re lessening their own risks as well as increasing their chance to generate income. If perhaps the individual really wants to invest their money in social websites, as an example, they are going to desire to make certain that is the correct decision for them.

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Investing in social websites is reasonably new, yet it’s nevertheless something somebody might achieve if they’re thinking about making use of social media to earn money. Someone may check the information published here to be able to discover a lot more now.

New Ways to Locate Extra Money in Your Budget

Many financial experts over here propose that men and women needing to reduce the level of their particular all round spending try and keep a diary of every dime they expend for just one month. After that 30 days, they need to go back and also sort out and also evaluate their buying over this time, and look for any patterns they might see. Until finally an individual chooses to participate in this kind of self-awareness activity, they are generally blind to simply how much money they tend to spend on unneeded plus frivolous objects. After they mount up the figures and also columns and do the math, they usually are determined to be able to conduct a more effective job as guardians across their own revenue.

For example, lots of discover that if and when they conserve his or her free change at the end of each day it makes for a significant sum after a while. Shopping originating from a actual list furthermore saves cash, as will acquiring shop brand names and also shopping for garments at thrift outlets. Acquire retail outlet phone apps for your most loved stores, and don’t obtain anything if it isn’t at discount. Regardless how you have established your financial budget, techniques like this can save you money. It really is really shocking, to discover just what number of methods somebody can easily utilize to save cash, even someone that considers they actually do a fantastic job regarding saving already.

Athens – Church of Agioi Theodoroi

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Crossing Odos Dragatsaniou, in the end stands the attractive medieval church of Agioi Theodoroi (St. Theodore), built on the site of a church founded in the ninth century, but in its present form dating from between 1050 and 1075. This small cruciform church with its high narrow dome, multiple roofs that lend it an air of rhythmic grace, narrow mullioned windows and decorated central door surmounted by arches, is a precious gem of eleventh century Byzantine architecture.

The earliest form of Byzantine churches was that of the basilica, a long rectangle divided by two or four ranges of columns into three or five naves. Later, during the 11th and 12th centuries, the plan changed to that of a Greek cross within a square, dominated by a dome constructed in brick and often combined with one or more subsidiary domes. The exterior walls consist of square-cut stone with thin brick surrounds and are enriched by bands of decoration, carving and the use of color. Few of these churches were large. Apart from St. Theodore, typical examples are the churches of Kapnikarea and St. Eleutherios.

The glory of the Byzantine church lies not so much in the architecture as to the ethereal beauty of its mosaics or frescoes. From the center of the principal dome Christ looks down upon the faithful and below Him are the Apostles. The Virgin appears in the half dome, while around the sanctuary are symbolic figures and emblems connected with the Eucharist. On the West wall opposite the chancel is the Last Judgement. Colored marble and similar material in the lower walls add to the resplendent beauty of the interior.

The liturgy of the Greek Orthodox Church requires separation of the altar from the laity. The altar is placed in a chancel screened from the congregation by the iconostasis, i.e. the screen dividing the sanctuary from the church proper. This is adorned with pictures of Christ, the Virgin, and Saints, and generally has three doors, the curtains of which are lowered while Mass is being celebrated. The chancel is flanked by the Prothesis, where the bread and wine for the Eucharist are prepared, and by the Diakonikon, or vestry.

In St. Theodore one can also notice the influence of the East on Byzantine art, which was prominent in the period from the mid-9th to mid-11th centuries, when Byzantine artists used a variety of Oriental motifs in their designs. It is probable that the design of pseudo-kufic characters (the script perfected during the 7th century by calligraphers in the city of Kafa, in present-day Iraq) that decorate the terracotta panel below the windows of the facade was inspired by the work of Arab craftsmen.

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Discover Exactly What To Contemplate Ahead Of Getting A Loan

When most folks begin to have a little bit of trouble with their money, they might look for short term loans to be able to see if they’re able to receive the assistance they will have to have to work through that hurdle. Whilst this really is advisable in certain situations, it is not always the very best plan. The person will probably wish to take their time to find out more with regards to their choices as well as to be able to ensure they really are making the correct choice for today as well as in the future. Naturally, even if the loan helps today, it isn’t advisable if it’s most likely to make their own finances worse with time.

Most people could receive a short term personal loan easily, even if they do not have an excellent credit history. If perhaps they’re merely finding it difficult for a solitary month caused by a problem that’s not very likely to reoccur, for instance a car wreck that will cause them to miss work, a loan may well be a good option. They should ensure they are going to be able to pay off the loan easily. In case they are, and the matter is only short-term, then a short term loan might be a wise decision for them.

Nonetheless, in case they will find they’re seeking to borrow money on a regular basis or in case they won’t have the ability to effortlessly pay back the loan, it’s usually not a good suggestion for an individual to receive one. Instead, they’re going to want to take a look at their own finances carefully in order to see precisely where the problem may be and also what they are able to do to fix it. More often than not, it’s feasible for a person to reduce the quantity they will spend and to get through the challenging period like that instead of receiving a loan they can’t easily pay off. It also could be a better idea to borrow a bit from family or friends because they could probably make smaller payments.

It really is critical for someone that is considering a short term loan to learn more to allow them to make certain they really are making the proper choice today and also for their future finances. Spend some time to read far more about this today and also acquire the aid you’ll have to have to make sure you remain at the top of your finances and don’t obtain financial obligations which will be challenging to repay.